Process for externally hardening cast iron and article of manufacture produced thereby



Patented Oct. 6, 1931 UNITED STATES PATENT OFFICE ADOLF FRY, of ESSEN, GERMANY, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THE NITRALLOY CORPORATION, A CORPORATION OF DELAWARE PROCESS FOR EZTERN'ALLY HAIREENING CAST IRON AND ARTICLE PRODUCED THEREBY No Drawing. Application filed January 30, 1928, Serial No. 250,729, and in Germany March 17, 1927.

The invention has for its object a process for hardening the marginallayers of cast iron, which process is carried out without any quenching operation and by which a cast iron is produced that is hard on its surface and possesses a particularly high resistance to wear. This object is attained according to the invention by subjecting a suitably alloyed cast iron (alloyed e. g. with aluminium) at comparatively low temperatures and for a sufficiently long time to the action of substances which give ofl nitrogen.

The process may be carried out for instance in the following manner: Cast iron articles are manufactured by casting into sand moulds, of a cast iron alloyed with about 1 per cent of aluminium. These aluminium-com taining cast articles after they have become cold may be brought into the desired finished shape by suitably machining them by means of cutting tools with the ease and in a similar manner as gray cast iron. After being machined, the cast articles are put into a, closed receptacle to which a gas is supplied that will liberate nitrogen, the receptacle having an outlet for the non-absorbed portions of the gas supplied. In this receptacle the articles are exposed at a temperature of about 500 degrees C. and for a sufliciently long time (more than 24 hours) to the action of gases containing, and capable of setting free, nitrogen. At this temperature the nitrogen penetrates into the cast articles, and according to the duration of the action of the nitrogen upon the cast articles, a more or less high degree of hardness of the surface of the articles is obtained. After the action of the nitrogen, the cast articles are slowly cooled without'quenching them. In this manner the surfaces of the articles may have imparted to them in a simple way hardnesses of about 650 to around 750-800 on the Vickers-Brinell hardness scale. These degrees of hardness approximately correspond to the Vickers- Brinell hardnesses of hard chill castings and secure a very high resistance to wear.

Besides aluminium, other elements that produce a definite improvement in the ability to acquire hardness by introduction of mtrogen when brought into contact therewith may be used as alloying additions. Examples of elements that may be so used are silicon, manganese, chromium, nickel, cobalt, vanadium, molybdenum, tungsten, titanium, zirconium and the like, either separately or in any desired combination. 1t will be understood that the proportions of these various elements that should be added to produce the desired nitriding effect will vary somewhat, depending upon the alloying element or elements used and further depending upon the results desired, such as for example whether a thick case is desired or a relatively thin casewith higher surface hardness. Consideration may also be given to the known properties of certain of the elements to efi'ect'structural im provement in the alloy being nitrided. In the case of the elements silicon and manganese, which are generally present in some amount in cast iron, it will be understood that the proportions of these must be increased to what in effect are alloying proportions as distinguished from normal proportions if reliance is to be had on these elements or either of these elements alone for promoting the nitriding effect.

The addition of aluminium, chromium, etc. to relatively low carbon steels and steel alloys, i. e., steels containing up to about 0.6% carbon, to improve their nitride hardening properties was disclosed in my earlier patents Nos. 1,487,554 and 1,649,398. However, when similar additions were made to such steels and steel alloys containing greater amounts of carbon it was found that the increased hardness due to the nitriding effect decreased with increasing carbon content, so much so as to indicate very clearly that if the nitriding treatment were to be applied to a ferrous alloy containing a carbon content characteristic of cast iron, no substantial increase in hardness would result. Consequently, it is surprising to find that when the carbon range characteristic of cast iron is reached, the addition of aluminium, or any one of the other alloying elements specified, either'alone or in any desired combination, is effective tobring about a definite improvement inthenit-riding properties.

When-in the following claims aluminium F MANUFAUI'UBQ alone is indicated as an alloying constituent, all substances are to be understood thereby, as for instance the above indicated ones, which produce the effect hereinbefore indicated.

It is to be understood that wherever in the claims the term compound is used in re ferring to the hardened layer suchterm is not limited to a definite chemical compound but may comprise a mixture of various chemical compounds, e. g., nitrides, which may be binary, ternary or more complex, and will ordinaril be present principally in the form. of a soli solution.

What I claim anddesire to secure by Letters Patent, is

1. The process comprising subjecting cast iron containing about 1 per cent of aluminum at a temperature of about 500 degrees C. to the action of a nitrogen-liberating substance.

2. The process comprising subjecting cast iron containing about 1 per cent of aluminium at a temperature of about 500 degrees C. more than 24 hours to the action of a nitrogen-liberating substance.

3. The process comprisingsubjecting cast iron containing about 1 per cent of aluminium at a temperature of about 500 degrees C. more than 24 hours to the action of a nitrogenliberating gas.

4. The process comprising subjecting cast iron containin about 1 per cent of aluminium and an a dition of at least one of the elements comprising the group: silicon, manganese,chromium, nickle, cobalt, vanadium, molybdenum, tungsten, titanium, zirconium, at a temperature of about 500 C to the action of a nitrogen-liberating substance.

5. The process, comprising subjecting cast iron containing about 1 per cent of aluminium and an addition of more than one of theelements selected from the group com-. prising: silicon, manganese, chromium, nickel, cobalt, vanadium, molybdenum, tungsten, titanium, zirconium, at a temperature of about 500 C. to the action of a nitrogen-liberating substance.

6. The process comprising subjecting cast iron, containing about lper cent of aluminium and an addition of a substance adapted to improve the strength of the cast iron, to

v the action of a nitrogen-liberating gas at a temperature of about 500 degrees C. more than 24 hours.

7. The process comprising subjecting cast 1ron, containing about 1 per cent of aluminium and another substance adapted to improve the ca acity of being hardened by nitrlding, of t e cast iron, to the action of a nitrogen-liberating gas at a temperature of about 500 degrees C. more than 24 hours. 8. An article hardened in its marginal layer by nitriding, and consisting of a cast'iron alloy containing about 1 per cent of aluminium.

9. An article hardened in its marginal layer by nitriding, consisting of a cast iron alloy containing about 1 per cent of aluminium, and as a further alloying addition at least one of the elements selected from the group: silicon, manganese, chromium, nickel,

cobalt, vanadium, molybdenum, tungsten, titanium, zirconium.

11. An article hardened in its marginal layer by nitriding and consisting of a cast iron containing an alloying addition having substantially the same properties as aluminium as regards ability to form with iron and nitrogen a hard compound when nitrided,

said addition being present in small but eflective proportions.

12, An article hardened in its marginal layer by nitriding and consisting of a cast iron containing an efiective and substantial proportion of an alloying addition, such as one or more of the elements aluminium, silicon, manganese, chromium, nickel, cobalt,

vanadium, molybdenum, tungsten, titanium, zirconium, "having the property of promoting the formation of a hard and adherent nitrided layer when such article is subjected to a nitriding treatment.

The foregoing specification signed at Cologne, Germany, this 13th day of January,

ADOLF FBY.

CERTIFICATE OF CORRECTION.

Patent No. 1,826,656. Granted October 6, 1931, to

ADOLF FRY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 18, claim -I, for "aluminiim" read aluminium; line 35, claim 4, for "nickle" read nickel,

and line 77, claim 10, for "conditions" read-additions; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record'of the. casein the Patent Office.

Signed and sealed this 8th dayol December, A. D. 1931.

a M. J. Moore, (Seal) Acting Commissioner of Patents. 

